[Pathogenomic surveillance of Bordetella pertussis clinical isolates in Liaocheng City, Shandong Province in 2024].

Objective: To analyze the molecular characteristics of prevalent Bordetella pertussis (Bp) isolates in Liaocheng City, Shandong Province in 2024. Methods: From March to August 2024, oropharyngeal swabs were collected from suspected pertussis cases at Liaocheng People's Hospital in Shandong Province for Bp isolation. A total of 99 Bp isolates were obtained. Whole-genome sequencing was performed on all isolates, followed by Multilocus Sequence Typing (MLST), vaccine antigen-related gene typing (including ptxP, ptxA, ptxB, ptxC, ptxD, ptxE, fhaB, fim2, fim3, and prn), 23S rRNA gene typing, and phylogenetic analysis. To capture the differences between Bp isolates and vaccine strains in Liaocheng City, the international vaccine strain Tohama I and the Chinese vaccine strain CS were included in the analysis. Antimicrobial resistance testing against 11 agents was performed on 52 isolates. Results: The throat swabs of 99 Bp isolates were collected from patients aged 44 days to 42 years, and the median age of the patients was 7 (5, 8) years. All isolates ptxP were ptxP3 type. 74 isolates (74.75%) carried the prn150, while 21 isolates (21.21%) were prn-deficient. The predominant antigenic profile was ptxP3/ptxA1/ptxB1/ptxC4/ptxD1/ptxE4/fhaB1/fim2-1/fim3-1/prn150, found in 72 isolates (72.73%). All 99 isolates carried the A2047G mutation in the 23S rRNA gene. Antimicrobial susceptibility testing showed that the MICs of macrolides and clindamycin for all 52 Bp isolates were all >256 mg/L. However, the isolates showed low MIC for seven other antimicrobials tested, including trimethoprim-sulfamethoxazole, amoxicillin, and levofloxacin. MLST typing revealed that 94 isolates (94.95%) were identified as ST-2, while 5 isolates (5.05%) belonged to a novel sequence type (ST-118). Phylogenetic analysis demonstrated that all 99 Bp isolates were highly homologous but clustered in evolutionary branches distinct from vaccine strains. Conclusion: In 2024, Bordetella pertussis isolates in Liaocheng City exhibit distinct clonal epidemic characteristics, with the predominant antigenic genotype being ptxP3/ptxA1/ptxB1/ptxC4/ptxD1/ptxE4/fhaB1/fim2-1/fim3-1/prn150. All isolates are resistant to macrolide antibiotics.